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Bayer Elastomer Provides The Finishing Touch

Bayer MaterialScience AG : 30 March, 2001  (Company News)
Thermoplastic polyurethanes (TPUs) from Bayer are contributing to the functionality, safety and appearance of a new line of electronic instruments from Tektronix, Inc., a leading provider of test, measurement and monitoring equipment for the communications and computer industries.
The Tektronix NetTek1 line of modular testing equipment features not only innovations in the instrumentation, but a novel combination of a die-cast magnesium case overmolded with Desmopan® thermoplastic polyurethane from Bayer. The TPU covering offers electrical insulating properties, and impact and moisture resistance, while providing a high- quality look and feel to the instruments.

David T. Engquist, a Mechanical Engineer at Tektronix, Inc., and one of the lead developers of the process and tools for overmolding the TPU on the NetTek instrument cases, said the combination of metal and elastomer met critical requirements. 'We didn't have anything like this - an overmolded magnesium case - in our industry. We wanted to utilize the shielding capability of the magnesium as well as the strength and torsional rigidity of die-cast metal, and we wanted the impact resistance we could get from an elastomeric material,' Engquist said.

'In the NetTek application, the Desmopan TPU provides impact and moisture resistance, mar and abrasion resistance, and the matte finish even helps with dissipating heat,' Engquist said. He said the TPU helped the instruments exceed the drop test specified in Bellcore GR-196-CORE.

'We also had a safety requirement, and Bayer's TPU provides a non-conductive layer around the instrument for added user protection. Bayer also facilitated a UL listing for the Desmopan material.'

Engquist said another benefit for Tektronix was using the elastomer to form the hinges for the doors, instead of needing separate parts and attachments. They were also able to mold in mounting features that otherwise would have required a separate, added bracket.

He also said the elastomer overmold gives the instrument a very high-tech look and feel. 'We were very pleased with the overall aesthetic,' Engquist said.

Innovative Engineering

The NetTek line consists of a base unit and attachable modules for differing measurement requirements. Currently, modules for the NetTek platform are available which allow the instrument to function as an Optical Time Domain Reflector (OTDR) or as a portable field tool for base station testing of wireless communication networks. The base, measuring 9 inches by 12 inches by 3 inches, is made of two magnesium castings, and each module is housed in another magnesium case, 7.5 inches by 9.5 inches by 1.5 inches, that plugs into the base.

Both the base unit and modules are overmolded with the Desmopan TPU, in thicknesses ranging from 1/16th inch to over _ inch. The TPU is injection molded over each case part and is held in position by a series of small teeth around the case and by holes either cast into the magnesium parts or tapped after casting.

Designing and executing the magnesium-TPU combination for the instruments took some time and innovative engineering, but according to Tektronix, actually saved money when compared to all-plastic cases with comparable capabilities.

'We didn't have to tool extra parts for attaching access doors to the units, and by using the magnesium for shielding, we didn't have to use an expensive conducting paint on a plastic part,' Engquist explained. 'Costs were also reduced because we eliminated the need for extra heat sinks and spreaders by thermally conducting to the metal.'

Gerald A. DiBattista, TPU Market Development Specialist for Bayer's Plastics Division, said Bayer's Desmopan and Texin® TPUs come in differing variations of hardness and durability, so manufacturers can choose the combination of properties that best fits their specific needs. 'These elastomers can be overmolded on just about any substrate, using either mechanical interlocks or through the material bonding directly to the substrate, and they are colorable,' DiBattista said. 'We have a broad range of TPUs, including not just aromatic but also aliphatic TPUs, which offer increased light and UV stability.'

'For the NetTek application, we were able to meet the requirements for the material itself and also provided technical support during design and production,' DiBattista said.
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